Process for the treatment of solid alkaline residue comprising calcium, heavy metals and sulphate

ABSTRACT

The invention relates to a process for the treatment of solid alkaline residue comprising calcium, heavy metals and sulphate, the process comprising: a)reacting the solid alkaline residue with carbon dioxide by contacting the solid alkaline residue with a carbon dioxide containing gas to obtain carbonated solid material; and c)washing the carbonated solid material with an aqueous stream to obtain washed solid material and wash water comprising calcium and sulphate and precipitating at least part of the calcium in the wash water as calcium carbonate.

FIELD OF THE INVENTION

The invention relates to a process for the treatment of solid alkalineresidue comprising calcium, heavy metals and sulphate, in particularincineration residue.

BACKGROUND OF THE INVENTION

Solid alkaline residues produced in many high temperature industrialprocesses, such as for example steel production, domestic wasteincineration and other incineration processes and combustion processes,may find application in the field of civil-engineering, for example asbuilding material, as foundation or embankment material in roadconstruction or as aggregate in concrete.

Bottom ash obtained in domestic waste incineration for example, is thecoarse residue that is left on the grate of the waste incinerator. Ittypically contains glass, ceramics, minerals, metals and some unburnedmaterial. Not all minerals obtained after the incineration process arethermodynamically stable and therefore, the material is susceptible toageing and weathering by atmospheric water, oxygen and carbon dioxide.As long as metastable minerals and mineral phases are present in thebottom ash, the material will undergo chemical and physical changes,resulting in for example leaching of heavy metals such as antimony,lead, copper, molybdenum and zinc and of salts such as chlorides andsulphates. Leaching of heavy metals to the environment is highlyundesirable. National authorities have therefore set limits for suchleaching. In order to meet the requirements for cationic metals, i.e.metals that exist mainly as cations in aqueous solutions, incinerationresidue is sometimes subjected to an accelerated weathering treatment,wherein the material is contacted with carbon dioxide in order toachieve so-called carbonation of the material. Carbonation is a chemicalreaction in which calcium hydroxide reacts with carbon dioxide and formsinsoluble calcium carbonate:

Ca(OH)₂+CO₂→CaCO₃+H₂O

In WO 94/12444 for example is disclosed a process for carbonation ofslags from waste incineration plants (WIP slags), wherein incinerationresidue is treated with a carbon dioxide-containing gas in order todecrease leaching of heavy metals like copper and lead. The leaching ofantimony, however, increases as a result of the carbonation treatment.

In ES 2137071 is disclosed a process for the stabilisation of inparticular zinc and lead in solid alkaline waste, by reacting the solidalkaline waste with carbon dioxide at a low pressure and for a shortresidence time.

Known carbonation processes, however, result in an increased leaching ofanionic metals (i.e. metals that exist mainly as anions in aqueoussolutions) such as for example antimony, chromium (as chromates) andvanadium (as vanadates). Leaching of salts such as chlorides andnitrates is not reduced by a carbonation process. Leaching of sulphatesstrongly increases due to the conversion of ettringite into gympsum thatis induced by carbonation. Carbonated material typically exceeds thelevels permitted by most national norms for leaching of sulphates andchlorides.

It has been proposed in the art to wash carbonated material with waterto reduce leaching of chlorides and sulphates. A problem with waterwashing, however, is that a large amount of washing water is necessaryin view of the low solubility and slow release of sulphate.

Therefore, there is a need in the art for a process for the treatment ofsolid alkaline residue, such as incineration residue, that not onlyresults in a reduced leaching of cationic metals from the material, butalso in a reduced leaching of sulphate and preferably also reducedleaching of anionic metals such as antimony.

SUMMARY OF THE INVENTION

It has now been found that leaching of salts, in particular the leachingof sulphates, from a solid alkaline residue, such as for example steelslag or residue of an incineration or combustion process, can be reducedby first subjected such solid alkaline residue to a carbonation step byreacting the solid residue with carbon dioxide to obtain a carbonatedsolid material, and then washing the carbonated material with an aqueousstream under such conditions that part of the washed out calcium isprecipitated. By precipitating washed out calcium, the amount ofsulphate that dissolves in the wash water and is therewith removed fromthe solid material, importantly increases.

Accordingly, the present invention relates to a process for thetreatment of solid alkaline residue comprising calcium, heavy metals andsulphate, the process comprising:

a) reacting the solid alkaline residue with carbon dioxide by contactingthe solid alkaline residue with a carbon dioxide containing gas toobtain carbonated solid material; and

c) washing the carbonated solid material with an aqueous stream toobtain washed solid material and wash water comprising calcium andsulphate and precipitating at least part of the calcium in the washwater as calcium carbonate.

An important advantage of the process according to the invention overwashing without calcium precipitation is that sulphate is dissolvedquicker and more completely and therewith a solid material with lessleachable sulphate is obtained. It will therefore be possible to use thetreated material in civil engineering applications without exceeding thelimits for allowable sulphate leaching to the environment. Moreover,less water will be needed for washing the same or even a higher amountof sulphate from the solid material.

In a preferred embodiment, the carbonated material obtained in step a)is mineralised before being washed in step c). In this mineralisationstep b), the carbonated solid material is contacted with anoxygen-containing gas for a period in the range of from 1 week to 12months, preferably at a mineralisation temperature in the range of from20 to 90° C. and preferably under conditions that the moisture contentof the material is kept between 5 and 20 wt %. In this mineralisationstep, anionic metals, in particular antimony, are fixated in thematerial resulting in less leachable anionic metals. Moreover,mineralisation typically results in a further increase in the amount ofleachable sulphate, so that more sulphate can be removed from thematerial in washing step c).

It is an advantage of the process according to the invention that thepreferred mineralisation temperature can be achieved without making useof an external heat source. This is achieved by making use of the heatgenerated by the exothermic carbonation and mineralisation reactions. Byfor example carefully choosing the dimensions of any depot or reservoirwherein the solid residue to be treated is provided, and carefullychoosing the flows of the carbon dioxide containing gas and theoxygen-containing gas used in steps a) and c), the mineralisationtemperature can be controlled.

DETAILED DESCRIPTION OF THE INVENTION

In the process according to the invention, solid alkaline residue istreated in order to decrease the amount of leachable components by firstcarbonating the material by contacting the solid alkaline residue with acarbon dioxide containing gas to obtain carbonated solid material(carbonation step a)) and then washing the carbonated solid materialwith an aqueous stream to obtain washed solid material and wash watercomprising calcium and sulphate and precipitating at least part of thecalcium in the wash water as calcium carbonate (washing step c)).Preferably, the carbonated solid material obtained in step a) ismineralised in a mineralisation step b) prior to being subjected towashing step c). Reference herein to decreasing the amount of leachablecomponents is to fixation of leachable components or to removal ofleachable components.

The solid alkaline residue may be any solid alkaline residue from anindustrial process involving very high temperatures, incineration orcombustion. Preferably, the solid alkaline residue is selected from thegroup consisting of steel work dust, steel slag, residues from anincineration process, and residues from a combustion process. Morepreferably, the solid alkaline residue is bottom ash from anincineration process, even more preferably bottom ash from incinerationof domestic waste or comparable waste.

Such solid alkaline residues typically are an assemblage of metastableminerals and mineral phases that include single or mixed oxides ofcalcium, magnesium, and iron and silicates, and further chlorides,sulphates, and heavy metals, such as zinc, lead, molybdenum, antimony,cadmium and copper.

In step a), the solid alkaline residue is carbonated by contacting theresidue with a carbon dioxide-containing gas.

In carbonation step a), cationic heavy metals such as for examplecopper, lead, zinc and cadmium are fixated in the solid material andsulphate and antimony are released from sulphate-containing mineralssuch as for example ettringite or from calcium-containing minerals suchas romeite. As a result, leaching of cationic heavy metals will decreaseand sulphate can be removed in a subsequent washing step to yield afinal material showing decreased sulphate leaching.

The carbon dioxide-containing gas may be any suitable carbon dioxidecontaining gas, for example a mixture of air and carbon dioxide, or aflue gas from a combustion process. Preferably, the carbondioxide-containing gas is a mixture of air and carbon dioxide, morepreferably a mixture of air and carbon dioxide comprising in the rangeof from 4 to 16 vol % carbon dioxide based on the total volume of themixture. In case flue gas is available at the location at which thecarbonation will take place, it may be advantageous to use the availableflue gas.

Carbonation of solid alkaline residue such as incineration residue iswell-known in the art. Any suitable carbonation conditions known in theart may be used.

The gas may be contacted with the solid residue in any suitable manner,typically by leading a flow of the carbon dioxide-containing gas througha depot of solid alkaline residue, for example by injecting the gas intothe depot. Such depot may be an open-air depot of solid residue or adepot in a container, such as for example a silo or a composting tunnel.Preferably, the flow of carbon dioxide containing gas through the solidmaterial is in the range of from 0.1 to 10 m³ gas per ton solid materialper hour, more preferably in the range of from 1 to 5 m³ gas per tonsolid material per hour.

Carbonation is preferably carried out until conversion of any calcium ormagnesium hydroxide or reactive calcium or magnesium silicate into itscorresponding carbonate is complete or substantially complete. Thedegree of conversion can suitably be monitored by determining the pH ofthe solid residue. This can for example be done by measuring the pH in aslurry of the solid residue in water. Preferably, carbonation is carriedout until the pH of the solid residue has decreased to a value in therange of from 8.0 to 8.5. Typically, in case of carbonation in largedepots with a height of e.g. five metres or more, a carbonation time inthe range of from 3 to 10 days, usually 4 to 7 days, will be required toachieve such pH decrease. It will be appreciated that the required timewill inter alia depend on the height of the depot, the temperature, thepressure, the concentration of carbon dioxide in the carbondioxide-containing gas, and the flow velocity of the gas through thesolid residue.

Step a) may be carried out at any suitable temperature, preferably at atemperature in the range of from 20 to 90° C., more preferably of from25 to 60° C. Any suitable pressure may be applied. Preferably, step a)is carried out at atmospheric pressure.

The carbonated solid material obtained in step a) is preferablysubjected to a mineralisation step b), prior to being washed in washingstep c), to obtain mineralised carbonated solid material. Inmineralisation step b), the carbonated solid material is contacted witha molecular-oxygen containing gas, preferably air. Preferably, the solidmaterial is kept at a mineralisation temperature in the range of from 20to 90° C. during the contacting in step b), more preferably in the rangeof from 40 to 60° C. Preferably, the solid material has a moisturecontent in the range of from 5 to 20 w %, more preferably of from 8 to15 wt %, during the contacting with oxygen-containing gas.

It has been found that if the temperature of the material is kept in thepreferred range of from 20 to 90° C., more preferably of from 40 to 60°C., and the moisture content of the material in the range of from 5 and20 wt %, preferably of from 8 to 15 wt %, antimony can be fixated to anextent that antimony leaching from the material can be kept below themaximum level allowed. A further effect of the mineralisation step isfurther release of sulphate from sulphate-containing minerals.

The oxygen-containing gas may be contacted with the carbonated solidmaterial in any suitable manner, typically by leading a flow of theoxygen-containing gas through a depot of carbonated solid residue, forexample by injecting the gas into the depot. Such depot may be anopen-air depot of solid residue or a depot in a container, such as forexample a silo or a composting tunnel. Preferably, the flow ofoxygen-containing gas through the solid material is in the range of from0.01 to 10 m³ gas per ton solid material per hour, more preferably inthe range of from 0.1 to 1 m³ gas per ton solid material per hour.Suitably, carbonation step a) and mineralisation step b) are carried outby first leading a mixture of carbon dioxide containing gas and airthrough a depot of alkaline solid residue and then, after sufficientcarbonation has taken place, continue with only leading air through thedepot.

Mineralisation will be carried out until sufficient mineralisation ofanionic metals, in particular antimony, has taken place. Referenceherein to sufficient mineralisation is to so much mineralisation thatantimony leaching of the mineralised material does not exceed theapplicable norms. The extent of mineralisation can be determined byperforming a leaching test, e.g. a column test or other leaching testknown in the art or required by the local authorities. Typically, themineralisation time needed for sufficient fixation of antimony and othermetals will be in the range of from 1 week to 12 months, preferably inthe range of from 2 weeks to 12 months, more preferably of from 6 weeksto 6 months. Although a relatively slow process step, it is asignificant acceleration compared to the speed of mineralisation bynatural weathering processes that occur if the material is stored in theopen air without further treatment.

Preferably, the temperature of the carbonated solid material is keptwithin the preferred mineralisation temperature range without using anexternal heat source. This can be done my making use of the heatgenerated during the exothermic carbonation and mineralisation reactionsthat take place in steps a) and b). By carefully choosing the dimensionsof the depot of solid material through which the gas is leaded andcarefully choosing the flow of gas through the solid material (in termsof volume of gas per weight per time unit), the heat generated issufficiently retained in the material in order to achieve the desiredtemperature.

It has further been found that a moisture content of the solid materialthat is contacted with the oxygen-containing gas in mineralisation stepb) below 20 wt % is preferred, more preferably below 15 wt %, even morepreferably below 12 wt %. It has been found that such relatively lowmoisture content results in an increased fixation of antimony.Preferably, the moisture content is not lower than 5 wt %, morepreferably not lower than 8 wt %. A moisture content in the range offrom 8 to 12 wt % is particularly preferred. If step b) is carried outat the preferred elevated mineralisation temperature (elevated comparedto ambient temperature) the desired moisture content can be achieved bycarefully choosing the dimensions of the depot of solid material throughwhich the gas is leaded and carefully choosing the flow of gas throughthe solid material, so that any moisture evaporated due to the elevatedmineralisation temperature can be discharged from the depot with the gasstream through the depot.

In step c) the carbonated solid material, preferably after amineralisation step b), is washed with an aqueous stream to obtainwashed solid material and wash water comprising calcium and sulphate. Atleast part of the calcium in the wash water is precipitated as calciumcarbonate. Washing with an aqueous stream may be carried out in anysuitable way, preferably by spraying the aqueous stream over a depot ofthe solid material and draining wash water from the bottom of the depot.

Calcium may be precipitated in the wash water before or after separationof the wash water from the washed solid material. If calcium isprecipitated after separation of the wash water from the washed solidmaterial, a calcium-depleted wash water is obtained that is recycled towash step c) to form part of the aqueous stream with which thecarbonated solid material is washed.

Preferably, at least part of the calcium is precipitated in the washwater by adding a carbonate salt to the aqueous stream used for washingthe solid material or by adding a carbonate salt or a carbonate-formingcompound such as for example carbon dioxide to the wash water afterseparation of the wash water from the washed solid material.

The carbonate salt may be any carbonate salt that is soluble in waterunder the conditions applied in washing step c), typically ambientconditions. The carbonate salt preferably is sodium carbonate, potassiumcarbonate or magnesium carbonate. In one preferred embodiment of theinvention, sodium carbonate is added to the aqueous stream used forwashing the carbonated solid material. As a result, the wash water willcomprises carbonate and at least part of the washed out calcium willprecipitate as calcium carbonate. The resulting lower concentration ofdissolved calcium in the wash water increases the solubility ofsulphate, which normally is present as gypsum, and therewith, moresulphate can be removed from the carbonated solid material and a lowervolume of aqueous stream is needed for removing sulphate.

Alternatively, the carbonated solid material may be washed with water asaqueous stream under simultaneous contacting of the carbonated solidmaterial with a carbon dioxide containing gas, for example pure carbondioxide or a mixture of air and carbon dioxide, preferably comprising4-8 vol % carbon dioxide. Calcium carbonate will then precipitate,typically on the solid material. As a result of the presence of carbondioxide, the pH of the water that is contacting the solid material maydecrease to a value below 7. If this is the case, the pH of the water isadjusted by adding an alkaline compound to the aqueous stream so thatthe pH of the water that is contacting the solid has a value in therange of from 7 to 8. In this embodiment (adding a carbon dioxidecontaining gas to the solid material), wash water separated from thesolid material may be recycled to the solid material to form part of theaqueous stream with which the carbonated solid material is washed.

Instead of adding a carbonate salt to the aqueous stream that iscontacted with the solid material or of adding carbon dioxide to thesolid material during washing, a carbonate salt or a carbonate-formingcompound such as carbon dioxide may be added to the wash water after ithas been separated from the washed solid material in order toprecipitate calcium from the separated wash water and obtaincalcium-depleted wash water. The calcium-depleted wash water thusobtained is then at least partly recycled to the carbonated solidmaterial to be washed to form part of the aqueous steam used forwashing. As a result of the recycling, the concentration of sulphate inthe aqueous stream and wash water will increase. After the sulphateconcentration in the wash water has achieved a predetermined level, forexample 1 wt %, wash water will be withdrawn from the process in orderto remove sulphates from the process.

In a preferred embodiment of the invention, a carbon dioxide containinggas is added to the wash water separated from the washed solid materialas a carbonate-forming compound. In order to achieve precipitation ofcalcium carbonate, the pH of the separated wash water needs to be in therange of from 7 to 8. If necessary, the pH of the separated wash waterto which carbon dioxide is added is adjusted to a value in the range offrom 7 to 8, preferably in the range of from 7.3 to 7.7, by adding analkaline compound, for example sodium hydroxide, to the separated washwater.

The aqueous stream preferably is water. The amount of carbonate salt orof carbonate-forming compound added to the aqueous stream or to theseparated wash water is preferably in the range of from 0.8 to 1.2 molecarbonate or carbonate equivalents per mole of sulphate to be removedfrom the solid material.

As a result of washing step c), the amount of leachable anionic metalsin the solid material, in particular antimony, may have increased.Therefore, it might be desirable to subject the washed solid materialobtained in step c) to a mineralisation step d). Step d) may suitably becarried out in the same way as hereinabove described for step b).Preferably, the washed solid material is kept at a temperature in therange of from 20 to 90° C. during the contacting in step d), morepreferably of from 40 to 60° C. Preferably, the washed solid material iskept at a moisture content in the range of from 5 to 20 wt %, morepreferably of from 8 to 15 wt %, even more preferably of from 8 to 12 wt% during the contacting in step d). In step d), however, an externalheat source might be required to achieve the preferred mineralisationtemperature and/or moisture content, since no use can be made of theheat generated in a preceding exothermic carbonation step.

The invention will be further illustrated by means of the followingnon-limiting examples.

EXAMPLES Example 1 Effect of Wash Step

Experiment 1—Washing with Water (Not According to the Invention)

Bottom ash from a domestic waste incinerator was washed with water byupwardly flowing a stream of 0.18 m³ of water per ton bottom ash per daythrough a container with bottom ash that was open at the top. The flowvelocity was such that wash water was allowed to flow away from the topof the solid material without entraining solid material. The washing wascarried out until 2.5 m³ of water per ton bottom ash had flown throughthe bottom ash.

The concentration of sulphate in the wash water separated from thebottom ash was determined by means of inductive coupled plasma emissionspectroscopy (ICP-ES) analysis at several points in time during thewashing step and the cumulative amount of sulphate washed from the solidmaterial (mg sulphate per kg dry bottom ash) at such point of time wascalculated.

Experiment 2—Washing with a Solution of Sodium Carbonate in Water(According to the Invention)

Bottom ash from a domestic waste incinerator was washed with a solutionof sodium carbonate in water (9.54 grams sodium carbonate per litrewater) by upwardly flowing a stream of 0.18 m³ of sodium carbonatesolution per ton bottom ash per day through a container with bottom ashthat was open at the top. The flow velocity was such that wash water wasallowed to flow away from the top of the solid material withoutentraining solid material. The washing was carried out until 1.0 m³ ofsolution per ton bottom ash had flown through the bottom ash. Thewashing was then continued with water until 2.5 m³ of aqueous stream(total of sodium carbonate solution and water) per ton bottom ash hadflown through the bottom ash.

The concentration of sulphate in the wash water separated from thebottom ash was determined by ICP-ES analysis at several points in timeduring the washing step and the cumulative amount of sulphate washedfrom the solid material (mg sulphate per kg dry bottom ash) at suchpoint of time was calculated.

Experiment 3—Washing with Recycled Calcium-Depleted Wash Water(According to the Invention)

Bottom ash from a domestic waste incinerator was washed by flowing astream of 0.18 m³ of water per ton bottom ash per day through acontainer with bottom ash that was open at the top. The flow velocitywas such that wash water was allowed to flow away from the top of thesolid material without entraining solid material. In a separate reactor,the wash water that was separated from the bottom ash was contacted witha flow of pure carbon dioxide gas with a velocity of 0.15 litres carbondioxide per litre wash water per hour, whilst the pH of the wash waterwas maintained at a value of 7.5 by addition of sodium hydroxide to theseparate reactor. The wash water was then separated from theprecipitated calcium carbonate and recycled to the bottom ash to serveas the water stream with which the bottom ash was washed. This washingwith recycled calcium-depleted wash water was carried out until 1.0 m³of solution per ton bottom ash had flown through the solid material. Thewashing was then continued with water until 2.5 m³ of aqueous stream perton bottom ash had flown through the solid material.

As in experiments 1 and 2, the concentration of sulphate in the washwater separated from the bottom ash was determined and the cumulativeamount of sulphate washed from the solid material calculated.

In FIG. 1, is shown the amount of sulphate (Y-axis; in mg sulphate perkilogram dry solid material) washed from the bottom ash as a function ofthe quantity of aqueous stream flown through the bottom ash (X-as; incubic metres aqueous stream per ton of solid material) for experiments1-3.

FIG. 1 shows that if the washing step is carried out under conditionsthat calcium precipitates in the wash water, a much lower volume ofaqueous stream is needed for the washing in order to remove the sameamount of sulphate.

Example 2 Effect of Mineralisation Step

Experiment a: carbonation step (1 week), followed by washing step,followed by post mineralisation step (8 weeks) as described hereinbelow.

Experiment b: carbonation step (1 week), followed by mineralisation step(2 weeks), followed by washing step, followed by post mineralisationstep (8 weeks) as described hereinbelow.

Carbonation Step

During one week a stream of 5 vol % carbon dioxide in air was led with aflow rate in the range of from 0.9 to 1.4 m3 per ton bottom ash per hourthrough bottom ash of a domestic waste incinerator that was kept in acontainer which was open at the top. The bottom ash was kept at atemperature of 40° C. and a moisture content of 15 wt % (based on thedry weight of the bottom ash)

Mineralisation Step

During two weeks a stream of air was led with a flow rate in the rangeof from 0.9 to 1.4 m³ per ton bottom ash per hour through the carbonatedmaterial obtained in the carbonation step. The bottom ash was kept at atemperature of 40° C. and a moisture content of 15 wt % (based on thedry weight of the bottom ash).

Washing Step

The carbonated or mineralised bottom ash was washed with water until aliquid/solid ratio of 8 cubic metres water per ton bottom ash wasreached.

Post Mineralisation Step

During eight weeks, the washed solid material (50 tons) was exposed tothe open air.

The copper, antimony and sulphate emissions from the solid material wasdetermined after each treating step by first leaching copper, antimonyand sulphate from the material by means of a batch leaching test withwater (liquid/solid ratio of 20 litres water per kg solid material) andthen determining the amount of leached copper, antimony and sulphate bymeans of ICP-ES analysis. In the Table is shown the results of thesemeasurements.

TABLE Emissions of Cu, Sb and sulphate after several process steps. Allemissions in mg per kg dry solid material Experiment a Experiment b CuSb SO₄ Cu Sb SO₄ Start 2.9 0.98 6,500 2.5 1.13 6,000 Carbonated 1.9 1.449,500 n.m. n.m. n.m. Mineralised n.a. n.a n.a. 1.2 0.80 8,000 Washed 1.00.86 2,600 0.87 0.61 1,670 Post mineralised 0.8 0.65 2,450 0.56 0.451,160 n.m.: not measured; n.a.: not applicable.

It can be seen from the results that a mineralisation step between thecarbonation and washing step results in a significant reduced amount ofantimony in the carbonated and mineralised material compared to thematerial that is only carbonated. The final emissions (in the postmineralized material) are clearly lower in Experiment b than inExperiment a. Further, the wash water obtained in Experiment b is lesspolluted than the wash water obtained in Experiment a and thereforeeasier to treat.

1-15. (canceled)
 16. A process for the treatment of solid alkalineresidue comprising calcium, heavy metals and sulphate, the processcomprising: (a) reacting the solid alkaline residue with carbon dioxideby contacting the solid alkaline residue with a carbon dioxidecontaining gas to obtain carbonated solid material; (b) washing thecarbonated solid material with an aqueous stream to obtain washed solidmaterial and wash water comprising calcium and sulphate and (c)precipitating at least part of the calcium in the wash water as calciumcarbonate.
 17. The process according to claim 16, wherein at least partof the calcium is precipitated in the wash water by adding a carbonatesalt to the aqueous stream.
 18. The process according to claim 16,wherein at least part of the calcium is precipitated in the wash waterby washing the carbonated solid material with an aqueous stream whileflowing a stream of carbon dioxide-containing gas through the carbonatedsolid material.
 19. The process according to claim 16, whereinprecipitating comprises: (i) washing the carbonated solid material withan aqueous stream comprising recycled wash water or water and recycledwash water; (ii) separating wash water from the carbonated solidmaterial to obtain the washed solid material and the wash watercomprising calcium and sulphate; (iii) supplying the wash water to aseparate container; (iv) adding a carbonate salt or a carbondioxide-containing gas to the wash water in the separate container toprecipitate part of the calcium and to obtain calcium-depleted washwater, wherein, in case a carbon dioxide-containing gas is added to thewash water, the pH of the wash water is adjusted to a value in the rangeof from 7 to 8 by adding an alkaline compound to the wash water; and (v)recycling the calcium-depleted wash water to the carbonated solidmaterial as part of the aqueous stream.
 20. The process according toclaim 16 further comprising: contacting, for a time period in the rangeof from 1 week to 12 months, the carbonated solid material obtained instep (a) with a molecular-oxygen containing gas, to obtain mineralisedcarbonated solid material, wherein in step (c) the carbonated solidmaterial is the mineralised carbonated solid material obtained in step(b).
 21. The process according to claim 20, wherein the molecular-oxygencontaining gas is air.
 22. The process according to claim 20, whereinthe solid material is kept at a mineralisation temperature in the rangeof from 20 to 90° C. during the contacting in step (b).
 23. The processaccording to claim 22, wherein the mineralisation temperature is in therange of from 40 to 60° C.
 24. The process according to claim 22,wherein no external heat source is used to achieve the mineralisationtemperature.
 25. The process according to claim 20, wherein the solidmaterial is kept at a moisture content in the range of from 5 to 20 wt %during the contacting in step (b).
 26. The process according to claim25, wherein the moisture content of the solid material is kept in therange of from 8 and 12 wt % during the contacting in step (b).
 27. Theprocess according to claim 16, further comprising: contacting the washedsolid material obtained in step c) with an oxygen-containing gas, for atime period in the range of from 1 week to 12 months.
 28. The processaccording to claim 27, wherein the washed solid material is kept at atemperature in the range of from 20 to 90° C. during the contacting. 29.The process according to claim 27, wherein the washed solid material iskept at a moisture content in the range of from 5 to 20 wt % during thecontacting.
 30. The process according to claim 16, wherein the solid,alkaline residue is bottom ash from an incineration process.